A few years ago, bittersweet randomly began growing in some of the evergreen trees at my family's farm. Probably thanks to a bird, the trees were bestowed with natural orange-red ornaments. We cut lengths of the vine for small arrangements inside the house...
My mom even wound some of it up in a circle and sent it to my apartment in a Fed Ex box. When it arrived and I removed it from the box, it was an accidental, ready-made bittersweet wreath. I took it from the box as-is and displayed it on the door, just in time for the holidays.
While I don't have photos of that bittersweet, here are a few from around the web to give you the idea. If you see some, don't hesitate to bring a cutting into your home for a little natural wintertime decoration. Note that the berries can be toxic, so don't leave them around your children or pets.
Images: 1: About.com, 2: an arrangement in a carrot (!) by Studio Choo at Design Sponge, 3: Farmhouse Musings, 4: paired with turquoise from Black Eyed Susan's Kitchen, 5: with carnations by Faith Durand / Apartment Therapy